feat: emit template-style route stubs (async, body param, service hint)

Add generate_routes(template_style=...) and CLI --template-style. When on,
stubs use async def, a JSON body parameter named body (dict or Model), and
with --inject-request a service-lookup hint comment before NotImplementedError.
Default behaviour (def/payload) unchanged. +2 tests (32 passed), wiki + MCP
bundle regenerated.

openapi_first/codegen_routes.pyi

@@ -8,4 +8,5 @@ def generate_routes(
     models_module: str = ...,
     inject_request: bool = ...,
     package: bool = ...,
+    template_style: bool = ...,
 ) -> list[Path]: ...